Background & Aims: The use of azathioprine and 6-mercaptopurine for inflammatory bowel disease increased in the early 1990s. We sought to determine the effect of this change in therapy on the risk of lymphoma in patients with inflammatory bowel disease. Methods: All patients with inflammatory bowel disease at a single tertiary care medical center who developed lymphoma between 1985-2000 were identified and the pathologic features of the lymphoma including presence of Epstein-Barr virus were determined. The patients were divided into two 8-year periods (1985-1992, 1993-2000) corresponding with the introduction of azathioprine and 6-mercaptopurine in 1993. Results: Eighteen patients with lymphoma were identified, 6 between 1985-1992 and 12 between 1993-2000. Six of 18 lymphomas occurred in patients treated with azathioprine or 6-mercaptopurine, all between 1993-2000. Seven patients developed Epstein-Barr virus-positive lymphoma (1 from 1985-1992, 6 from 1993-2000). Five of 7 Epstein-Barr virus-positive lymphomas occurred in patients treated with azathioprine or 6-mercaptopurine compared with 1 of 11 Epstein-Barr virus-negative lyrephomas (P = 0.01). Approximately 1200 patients with inflammatory bowel disease were treated with these agents between 1993-2000. Conclusions: Treatment of inflammatory bowel disease with azathioprine or 6-mercaptopurine appears to be associated with a small increased risk of Epstein-Barr virus-positive lymphoma.
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